There exists a need for isolation and/or protection of patients, doctors, nurses, visitors, people in close proximity to toxic materials etc. from obtaining airborne diseases or intoxication due to microorganisms, viruses and/or hazardous particulate matter spread via the air. The need for protection of healthy people or the need for cleaning exhaled air is obvious with respect to highly infective viruses such as the flu virus A H1N1 or other swine influenza viruses such as mutated swine influenza viruses, SARS (Severe Acute Respiratory Syndrome) or other coronaviruses, highly pathogenic H5N1 virus or other bird influenza viruses, such as other mutated bird influenza viruses, terrorist attacks with biological weapons (anthrax, small pox), drug resistant tuberculoses, staphylococci etc. Also with respect to the persons suffering from less severe diseases, the protection of those people taking care of the patients or protection of the patients themselves may be of crucial importance to reduce the risk for the patients to catch other diseases.
Ventilation by aspirating air through an exhaust e.g. located in the ceiling is generally used for performing indoor cleaning of air. However, the airflow towards the exhaust opening is not effective for removing contaminated air delivered by e.g. a diseased patient 1-4 m from the exhaust opening.
In respect of the airflow close to the exhaust, the contaminant-capturing efficiency of an exhaust depends on the exhaust design, the positioning near the contaminant source (e.g. sick patient with airborne contagious disease) and the exhaust airflow. The flow of a point exhaust can be used to approximate the air flow in the vicinity of an exhaust opening projecting over a surface. A point sink will draw air (Q) equally from all directions through an area equal to that of an imaginary sphere of radius, r. The radial velocity, vr, of the sink is given as: vr=Q/(4 πr2). The air movement in the vicinity of exhausts is quite complex. Generally, the air velocity distribution across an exhaust surface is not uniform and is influenced by wake formation near the sides of the exhaust or flow contraction, which results in reduction of the effective face area of the exhaust. This leads to fast velocity decay as moving further away from the exhaust surface (FIG. 24).
An alternative to ventilation by exhausting air has been to use isolation rooms for patients being infected by life-threatening airborne diseases. Generally, the aim of infectious isolation unit/room ventilation is to protect or isolate the rest of the hospital from airborne transmission of pathogens exhaled or coughed by the sick patients. Nevertheless, medical staff working in infectious isolation units is under elevated risks of getting sick and spreading the disease. Recent multi-drug resistant strains of tuberculosis have increased the importance of air change rates, filtration, air distribution designs and pressurization.
Today, in infectious wards mixing type of air distribution is used. This can be obtained by exhausting air from a room through ventilation diffusers positioned in or just below the ceiling of the room and at the same time supplying the room with clean air. The clean air supplied at high velocity promotes mixing of the air in the room, and thus dilutes the airborne pathogens and evacuates them out of the room. The problem is that with perfect mixing the concentration of pathogens in the room would be the same in the whole occupied space. Hence to reduce the risk of airborne transmission of infection one needs high air change rates. The more air supplied, the better the dilution. Air-changes of minimum 12 per hour are recommended for isolation hospital wards to dilute the airborne pathogens (ASH RAE Handbook 2007, ISIAQ Review 2003). Some guidelines even recommend as much as 15 air changes per hour as a minimum requirement (WHO 2002). It is evident that the recommended high flow rates will imply quite a lot of energy consumption to condition the air in isolation rooms within the recommended range of indoor temperatures of 21-24° C. Also the ducting, fans and HVAC (heating, ventilation and air-conditioning) unit required for the ventilation systems would be expensive and would occupy quite a lot of space. Another important issue is that this kind of ventilation works with 100% outdoor air, which additionally raises the running costs of the units and make them quite energy inefficient. Use of HEPA filters themselves could become source of secondary spread of pathogens if not changed on regular bases. Usually they are situated out of the ventilated area which elevates the risk of contamination and thus infection. This is another cost related issue for the maintenance of such a system. The use of UVGI when placed in the ventilated area is not quite efficient because the source generating pathogens is located in the lower height of the ventilated space while the UVGI unit for safety reasons is typically installed far way in the upper zone (not lower than 1.7 m above the floor).
Some of the pulmonary activities, i.e. coughing/sneezing, generate quite strong air movement with initial velocities as high as 30 m/s, that completely destroy the ventilation air pattern in the rooms and enhance the airborne cross-infection risk among occupants. To remedy the problem inherent in hospital ventilation systems for infectious isolation units the present invention can be incorporated in the patient's bed or can be secured to the patient's bed. The ventilation units close proximity to the head of the sick person guarantees successful evacuation of the largest part of the pathogen laden air from pulmonary activities, purging it and directing it e.g. upwards, through one or more horizontal slots, towards the exhaust vents of the total volume ventilation at elevated velocities.
Especially in hospitals, crowded and highly visited places and other buildings or equipments subjected to ventilation, the method described herein may allow for considerable energy savings otherwise used for conditioning outside air supply, by reducing as much as two times the need of fresh air for the total volume ventilation. Furthermore, the method ensures much cleaner air in rooms compared to mixing ventilation alone, and thus reduces airborne transmission of infectious diseases to the hospital staff (doctors, nurses, etc.), in clean rooms to immunocompromised patients (HIV positive or with congenital immune disorders), or in other rooms or areas where people may come close to each other.
Herein below a situation as well as a simulation of air distribution from a hospital is described, although the invention herein described can be used in different applications or locations where people come relatively close to each other or come into contact with each other. Examples of such applications or locations where the filtration/ventilation unit or a combination of several units and the system described herein can be used are in hospitals of different kinds, aeroplanes, waiting rooms, trains, busses, restaurants, dental clinics, beds in hotels, beds in homes for elderly people, wheelchairs, nurseries, animal farms (installed for protecting farmers and animals), public toilets etc. However, the filtration/ventilation unit as described herein can also be used to protect subjects and individuals with weak immune system, in the handling of food or food ingredients or in the production and/or wrapping up of food ingredients, food, beverages, pharmaceuticals (pills, vaccines etc), cosmetics, electronic and computer components etc. The filtration/ventilation unit can also be used to remove flavours and/or smells generated in kitchens or kitchen areas, productions that involve handling of obnoxious gases or smells, etc.
Prior art products exists which are ventilators that clean the air, however, these ventilators do not produce an air curtain which can be used to partly or fully isolate an individual which is diseased, or which is at risk of obtaining a disease due to the spread of airborne infections.
When handling food products and infectious air gets into contact with the food ingredients, food or beverages a contamination may occur making the product unsalable due to growth of microorganisms, etc. or the product may become unsafe to eat. The filtration/ventilation unit as described herein may thus be used for a large number of applications within food products or food production such as exhaust of micro-organisms, etc., exhaust of flavours, inflow of air or gas e.g. a gas with a specific composition such as air with an increased amount of oxygen, shielding of one or more individuals, shielding of items such as food products.